Books LIKE Stargate?

Can we talk about books LIKE Stargate, that aren't Stargate books? Ones that mix history and mythology research with sci-fi and modern day ethical dilemmas, maybe a bit of action/suspense, and stuff like that?

It might be a broad topic, but I'm sure we can just list the best/closest.

I saw someone mention Arthur C Clarke's Rama series. I'd definitely add Childhood's End to that (although I've only seen the TV mini-series so far).

Any other recommendations? Personally, I'm open to sci-fi, fantasy, sci-fi/fantasy, X-Files-like conspiracy investigation (to a point) and (again, to a point) horror -- especially Lovecraftian-style stuff.